Question

A man can do a piece of work in 5 days. He and his son working together can finish it in 3 days. In how many days can the son do it alone? 1

(a) $6\frac{1}{2}$ days

(b) 7 days

(c) $7\frac{1}{2}$ days

(d) 8 days

Answer 1

A man's 1 days work $=\frac{1}{5}$

Man and his son's 1 days work $=\frac{1}{3}$

$\therefore$ Son's 1 days work $=\frac{1}{3}-\frac{1}{5}$

$=\frac{5-3}{15}=\frac{2}{15}$

$\therefore$ His son will finish the work

$=\frac{15}{2}day=7\frac{1}{2}$ days